fix: workflow tool file error

[Nov1c444]

Summary

When using workflow as a tool, if a parameter of type file is returned, it will cause an error.
The reason is that Pydantic will attempt to validate each type in the union type sequentially. Now, after adjusting the order of the union types, the issue is resolved.

Screenshots

Before	After

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods